1. Field of the Invention
The invention relates to a cathode material particle, and more particularly a cathode material particle with a plurality of cores individually covered uniformly with a nano-metal oxide layer to improve the safety when used on a lithium battery.
2. Description of Related Art
High-capacity cathode material used on a lithium battery not only affects the battery characteristics, but also influences the safety of the lithium battery. In addition to the requirement the high-capacity, thermal stability is an important factor for the safety of the cathode material. The cathode material must be very safe when used on the lithium battery. A new cathode material is lithium-nickel oxide (LiNiO2) that has high-capacity but is unsafe and poor cycleability. Therefore, the lithium-nickel oxide is difficult to use with lithium batteries presently. Another cathode material is lithium-manganese oxide (LiMn2O4) that is safe for lithium battery but only has a capacity of about 110 m-Ah/g (milliampere hour/gram) that is 40%-45% lower than the capacity of still another cathode material of lithium-cobalt-nickel oxide (LiCoNiO2).
Lithium cobalt nickel oxide is a potential material for cathode material but has not been merchandised because the safety problem has not been resolved. To overcome the safety problem with lithium-cobalt-nickel oxide, metal ions such as aluminum or magnesium ions are doped into the lithium-cobalt-nickel oxide to improve the safety. However, the capacity of the cathode in the lithium batteries is reduced and internal resistance is increased so that the lithium batteries can not discharge and charge in high-rate. Alternately, a metal oxide layer can be coated on sintered lithium-cobalt-nickel oxide particles by secondary sintering. However, the thickness of the metal oxide layer is on the order of a micron that increases the surface resistance of the cathode and increases non-charging areas to the lithium-cobalt-nickel oxide. Therefore, the cathode material made of lithium-cobalt-nickel oxide with a micron metal oxide layer also has the problems of increasing internal resistance, decreasing capacity of high-rate discharge, etc.
With reference to FIG. 9, U.S. Pat. No. 6,733,923 disclosed a battery (20). The battery (20) has an aluminum (Al) foil (21), two electrodes (22) is and two porous oxide layers (24). Each electrode (22) comprises a plurality of particles (23). A thickness of the electrode (22) is about 50 μm to 10 μm. The porous oxide layers (24) are respectively covered on the electrodes (22). The porous oxide layers are just only coated on the surface of the electrode (50˜100 μm), the coating layer will swell during electrode cycling test.
The present invention has arisen to provide a cathode material particle on the order of nanometer thickness to mitigate or obviate the drawbacks of conventional cathode material.